Electrolytic cellulose recovery apparatus



Oct. 9, 1956 .JQF. ESTES 766,202

ELECTROLYTIC CELLULOSE RECOVERY mARATUS Filed Jan. 18, 1952 ELacTzou mc CELLS 70 20 v H L F I all i GAS 1 7 J Gournovd CHEMICAL5 72 Racoveczy 2/ T 23 K 22 FlG.l

IN V EN TOR.

y ATTORNEY ELECTRDLYTEC CELLULOSE RECOVERY APPARATUS Joseph F. Estes, New York, N. Y. Application January 18, 1952, Serial No. 267,173

4 Claims. (Cl. 204-242) This invention relates to apparatus for recovering cellulose from cellulose containing materials.

An object of this invention is to provide apparatus particularly adapted to treat waste cellulosic materials such as bagasse, hemp and flax hurds, sisal and abac. waste, and the like to recover therefrom substantially the entire cellulose content thereof without extensive and prolonged pre-cooking of the waste material.

Another object of this invention is to provide apparatus including electrolysing means for depositing from a cellulose containing solution, pure cellulose which contains beta and gamma cellulose, as well as alpha cellulose.

A further object of this invention is to provide apparatus for producing pure cellulose, free from discoloration and in the form of finely divided particles entirely free of cellulose in fibrous form.

Still another object of this invention is to provide apparatus for electrolytically depositing cellulose and including improved cell means adapted to insure a final product free of discoloration and of uniform physical and chemical characteristics.

Still a further object of this invention is to provide apparatus for recovering pure cellulose from cellulose solutions by electrolytic means, wherein said apparatus is arranged for continuous operation whereby the cellulose solution may be continuously circulated while undergoing electrolysis and the several constituents of the solution may be replaced as they are removed from the solution.

Other objects of this invention will in part be obvious and in part hereinafter pointed out.

The invention accordingly consists of the elements of construction, arrangement of parts and interconnection of devices as will be exemplified in the embodiment hereinafter described and of which the scope of invention will be indicated in the claims following.

In the drawing;

Fig. l is a diagrammatic illustration of the system embodying the invention;

Fig. 2 is a vertical sectional view of an electrolytic cell embodying the invention;

Fig. 3 is a perspective view of the anode assembly thereof.

Referring in detail to the drawing, and particularly to Fig. 1, 1t) designates a cellulose recovery system embodying the invention. The same comprises a plurality of similar electrolytic cells 11, shown as three in number for the purpose of illustration. The cells are arranged in adjacent relationship for interconnection. Thus, a liquid outlet 12 located at the top of each cell, is connected to a liquid inlet 13 of an adjacent cell; such inlets being located at the bottom of the cell.

Each cell 11 is provided with a removable, gas tight cover 14 having an outlet 15, for the purpose hereinafter described.

The cells 11 are adapted to have a cellulose containing solution continuously circulated therethrough. Accordingly, there is provided a solution supply tank 16 which is connected at the bottom thereof to the liquid inlet of one end cell by a pipe line 18 and which is further connected at the top thereof to the liquid outlet of the other end cell by a pipe line 17. A pump, not shown, may be used to provide circulation of the solution at pressures ranging between 2 to 5 pounds. Valves may be inserted at suitable points in the circulatory system for controlling the operation thereof.

The cellulose solution which is to be treated may be of the type more fully disclosed in application Ser. No. 266,799, filed January 16, 1952. Such solution may include various waste cellulosic materials such as bagasse, hemp and flax hurds, sisal and abaca waste, as well as cotton or linen rags, and ramie. It is understood that various :other cellulose containing materials, including cotton fiber or linters may be used. The cellulosic mate rial may be given a preliminary treatment with relatively weak solutions of sodium hydroxide, sodium sulfate, sodium sulfite or weak alkali solutions. Such treatment is of rather short duration and removes lignin, as well as other impurities including pectin, wax, fats and the like. However, such treatment does not remove from the cellulosic material, the beta and gamma cellulose content thereof.

As disclosed in the above referred to application, there is provided a cellulose dissolving solution made essentially by mixing a saturated solution of a metal salt, such as copper sulfate containing ammonium chloride, with a concentrated sodium hydroxide solution to form a green precipitate which is then dissolved in ammonium hydroxide to form the required solution.

The prepared cellulosil material is dissolved in the solution and is supplied to tank 16. During the course of the electrolytic action in cells 11, gases including ammonia will be evolved and such gases are recovered in a gas recovery tank 19 which is connected to outlets 15 of the cells by a pipe line 20. The recovered gases are reintroduced into the circulating solution by connecting tanks 16 and 19 with a pipe line 21. Other chemical constituents of the solution are lost during the course of electrolysis, as will be more fully described, and accordingly, a third tank 22 is provided for supplying chemicals in replaceemnt of those lost, through a pipe connection 23 to tank 16.

As shown in Figs. 2 and 3, each cell 11 is provided with sheet cathodes 24 of copper, which are securely fastened to opposite side walls of the cell. A single anode 25, which is in the form of a substantially rectangular sheet or plate of iron, is removably mounted in each cell and located between the cathodes thereof and equidia tantly thereof.

As shown particularly, in Fig. 3, the anode 25 is mounted in an assembly including a pair of flat striplike members 26 which may be longitudinally grooved at their mid section to receive the side edges of the anode. A semicylindrical member 27 is longitudinally grooved on a mid portion of its planar surface to receive the bottom edge of the anode, such member extending to the side members 26. It will be apparent, that members 26, 27 form shelflike portions relative to the opposite surfaces of the anode, for the purpose hereinafter described. The upper end of the anode projects above the top edges of members 26 and is formed with an opening 28 for receiving a hook or other means for removing the anode assembly from the cell.

The end walls of the cells 11 are for-med with vertical slots for slidably receiving the members 26 or" the anode assembly. Such slots terminate at their lower ends short of the bottom wall of the cell whereby member 27 of the anode assembly is located in spaced relation to the bottom wall of the cell.

In operating the system, a solution of dissolved cellulose containing material is placed in tank 16 and is circulated through the cells 11, the anodes and cathodes of which are suitably connected to a direct current source. The current may have a voltage ranging between 2 to 12 volts and a current density ranging between 2 and 20 amperes per square foot of exposed anode surface.

The total number of cells used, their relative size and the rate of liquid circulation may be varied in terms of the currents used and the type of end product desired. Thus, it has been found that with current densities of l15 amperes per square foot, there is formed on the anodes a gelatinous cellulose mass which is retained on the anode when the same is removed from the cell, due to the members 26, 27 which frame the anode. Such gelatinous mass is scraped off the anode, washed with water and dried to form a finely divided product which is free of discoloration or any cellulose in fibrous form. Furthermore, such product will contain the beta and gamma cellulose, as well as the alpha cellulose corresponding to that found in the original cellulose containing material which is treated. With lower amperages, the final product will be of a rubbery nature. Any residual impurities in the cellulose solution including lignin, pectin, oils, and the like, fall to the bottom of the cells and may be periodically removed through sludge removal lines, not shown.

It has been found that the apparatus operates at maximum efiiciency when anodes are used which are made of a copper bearing iron. An iron having the following analysis: iron-99.874; carbon.01l; manganese.0l7; sulfur-.032; phosphorus.008; copper--.030; and gases-.028, all percent, used as an anode, resultants in a cellulose product which is free of any discoloration. Such anodes are also particularly resistant to the action of the solution. The members 26, 27 may be made of inert materials such as hard rubber, or the like.

As the solution is electrolyzed in cells 11, gases including ammonia, will be evolved and are recovered in tank 19. Since the solution will show a reduction in ammonia content, the recovered gases are reintroduced into the circulating solution to substantially restore the gaseous ingredients thereof to normal.

It will be apparent, that as the electrolytic action continues, the metallic components of the cellulose solution such as copper, zinc, nickel or the like, will be deposited on the cathodes of the cells. Accordingly, to restore the metal balance of the circulating solution, cellulose dissolving solution prepared as previousiy described, except for the ammonium hydroxide, is supplied from tank 22 to tank 16, as required.

As cellulose is deposited on the anodes, the cellulosic content of the circulatinig solution is restored to a predetermined level, by periodic addition of cellulose containing material to tank 16 Where the same is quickly dissolved in the solution. It has been found that operation of the system is highly efiicient when a single cycle of solution circulation through the cells results in a deposition of substantially 50% of the cellulose content thereof.

Periodically, the circulatory system may be halted to allow the deposited metal on the cathode to be either removed or kicked back into solution by the use of a reversed direct current used alternatively with an alternating current. With copper cathodes, the metal content of the cellulose solution may be modified, without materially aifecting the operation.

The curved surface of member 27, being located opposite the liquid inlet 13 in each cell, forms a bafiie and prevents any undue turbulence in the incoming cellulose solution. This permits more uniform action in the electrolytic cell as well as preventing the newly deposited cellulose on the anode surface from being dislodged therefrom.

The connections between gas outlets 15 on the cell covers 14 and the pipe line 20, may be such as to allow the covers to be readily removed from the cells when the anodes are to be removed to allow the deposited cellulose to be scraped off.

It will thus be seen that there is provided in accordance with the invention disclosed, improved apparatus for recovering cellulose of a high degree of purity, free of discoloration and cellulose in fibrous form and on an economical basis, thus achieving the several objects of the invention.

As various possible embodiments might be made of the above described invention, it is understood that all matter herein set forth or shown in the accompanying drawing, is to be interpreted as illustrative and not in a limiting sense.

Having thus described my invention, I claim as new and desire to protect by Letters Patent:

1. In combination, an electrolytic cell for recovering pure cellulose and a removable anode comprising a substantially rectangular plate of metal, means framing the side and bottom edges of said plate and including portions projecting from opposite faces of said plate and means on opposed inner surfaces of said cell for slidably engaging the side framing means whereby said anode may be inserted into and removed from said cell.

2. The combination as in claim 1 wherein said framing means includes a portion at the bottom of said anode for reducing turbulence of liquid entering said cell.

3. The combination as in claim 1 wherein said last mentioned means comprises slots formed in opposite cell walls and terminating at their lower ends short of the bottom of the cell.

4. In an electrolytic cell for depositing pure cellulose, an anode comprising a rectangular sheet of iron, a pair of inert members respectively engaging the side edges of said sheet with portions projecting normally of either face of said sheet and a semicylindrical member with the planar portion thereof engaging the bottom edge of said sheet and forming a projecting shelf relative to the faces of said sheet.

References Cited in the file of this patent UNITED STATES PATENTS 525,303 Woods Aug. 28, 1894 546,873 Ashcraft Sept. 24, 1895 1,137,874 McCaskell May 4, 1915 1,588,679 Hale et al. June 15, 1926 1,590,606 Taylor June 29,1926 2,343,161 Tetrault Feb. 29, 1944 OTHER REFERENCES Corrosion Resistance of Metals and Alloys, by McKay et al. (1936), pages 242, 243. 

1. IN COMBINATION, AN ELECTROLYTIC CELL FOR RECOVERING PURE CELLULOSE AND A REMOVABLE ANODE COMPRISING A SUBSTANTIALLY RECTANGULAR PLATE OF METAL, MEANS FRAMING THE SIDE AND BOTTOM EDGES OF SAID PLATE AND INCLUDING PORTIONS PROJECTING FROM OPPOSITE FACES OF SAID PLATE AND 